Supplementary Materials for
Reversing the chirality of cellulosic nanomaterials
Kevin Conley, Louis Godbout, M.A. Whitehead, Theo G.M. van de Ven*
*Correspondence to:
Characterization of peeled cellulose nanomaterials
The cellulose nanomaterials were chemically peeled with a sequential periodate-chlorite oxidation discussed in detail elsewhere (Conley et al. 2016). The change in size of the cellulose nanomaterials after periodate-chlorite chemical peeling was most evident in TEM as seen in Figure S1.
The carboxylic charge content introduced by the periodate-chlorite oxidations was obtained by conductometric titration (Araki et al. 2001, Habibi et al. 2006) using a Metrohm 836 Titrando Instrument. Although the highly water soluble oxidized surface chains detach from the crystal and are removed from the suspension, the carboxylic acid content increases with increased oxidation as seen in Tables S1-2. As discussed extensively in (Conley et al. 2016), the periodate oxidation proceeds at two crystal fronts – from the sides and at the crystal ends. When a surface chain has been oxidized to a sufficiently water soluble polymer, the chain detaches from the crystal and is removed from the suspension. Some partially oxidized chains react at the crystal ends but are anchored to the crystal core. These chains cannot detach and are not solubilized. This reduces the observable length in TEM, but gives the nanocrystals charged dangling chain ends. These hairs do not participate in the binding of Congo red. Solublilized DCC does not induce circular dichroism as seen in Figure S2.
Figure S1. The change in dimensions of cellulose nanocrystals after chemical peeling. A) Unmodified CNC from spray-dried wood source. Carboxylic acid content is 0.1 mmol COOH /g. (width = 16.3 ± 4.6 nm, length = 160 ± 66 nm). B) Peeled DCC-CNC with an initial aldehyde content of 4.3 mmol/g. Carboxylic acid content is 0.4 mmol COOH /g. (width = 8.2 ± 2.2 nm, length = 88 ± 36 nm). Error reported as standard deviation. Scale bar = 500 nm.
Figure S2. Electronic spectra of DCC. A) Absorption spectra of fully solubilized 2,3-dicarboxyl-cellulose in the presence of Congo red (0.34% DCC; 18.5 μM CR), Congo red (18.5 μM), and conventional CNC in the presence of Congo red (1.85% CNC; 18.5 μM CR). B) Induced circular dichroism of Congo red by fully solubilized 2,3-dicarboxyl-cellulose (0.34% DCC; 18.5 μM Congo red). Degree of substitution of 0.9. No circular dichroism is induced.
Table S1
Dimensions and charge content of peeled cellulose nanocrystals from spray dried wood source
Width (nm) / Length (nm) / Charge content (mmol COOH/g)16.3 / 160 / 0.1
14.3 / 160 / 0.3
13.4 / 140 / 0.3
10.9 / 110 / 1.4
9.0 / 80 / 2.0
8.2 / 90 / 0.4
Table S2.
Dimensions and charge content of peeled cellulose nanofibrils
Width (nm) / Length (nm) / Charge content (mmol COOH/g)7.5 / 1000 / 1.2
5.4 / 700 / 0.5
Induced circular dichroism of peeled cellulose nanomaterials
The induced circular dichroism spectra of the CNC and CNF suspensions (1.85% CNC or 0.15% CNF; 18.5 μM Congo red) of various widths are shown in Figure S3. As the cellulose nanocrystals are thinned, the peak at 525 to 550 nm and 440 nm gradually reduces in intensity before reversing sign. The peak intensity is presented in Figure 2, main text. The circular dichroism reverses as the chiral surface acts as an enantiomer sink, trapping the opposite Congo red rotational isomer. CNF directly prepared from fibers is left-handed. Different aliquots of the same suspension did not appreciably change the induced circular dichroism as seen in Figure S4.
A)
B)
Figure S3. Induced circular dichroism of peeled cellulose nanomaterials. A) bundled cellulose nanocrystals from spray-dried form (1.85% CNC; 18.5 μM Congo red), B) Cellulose nanofibrils (0.15% CNF; 18.5 μM Congo red).
Figure S4. Induced circular dichroism of two aliquots of a suspension of bundled cellulose nanocrystals from spray-dried form (1.85% CNC; 18.5 μM Congo red)
References
1. Conley, Kevin, M. A. Whitehead, and Theo GM van de Ven. "Chemically peeling layers of cellulose nanocrystals by periodate and chlorite oxidation." Cellulose 23.3 (2016): 1553-1563.
2. Araki, Jun, Masahisa Wada, and Shigenori Kuga. "Steric stabilization of a cellulose microcrystal suspension by poly (ethylene glycol) grafting." Langmuir 17.1 (2001): 21-27.
3. Habibi, Youssef, Henri Chanzy, and Michel R. Vignon. "TEMPO-mediated surface oxidation of cellulose whiskers." Cellulose 13.6 (2006): 679-687.